Question

Calculate the answers of the following questions by using mental calculations.

(i) (a) 68² - 3²

(b) (31\(\frac{1}{2}\))² - (2\(\frac{1}{2}\))²

(c) 3.6² – 1.4²

(ii) (a) 201 × 99

(b) 2\(\frac{1}{3}\) x 1\(\frac{2}{2}\)

(c) 10.7 × 9.3

Answer 1

(c) 10.7 × 9.3

= (10 + 0.7) (10 – 0.7)

10² – 0.7²

= 100 – 0.49

= 99.51